The dye is found in many foods, such as Doritos corn chips. Photo / 123rf
The dye is found in many foods, such as Doritos corn chips. Photo / 123rf
Rubbing an E-number found in the orange food dye used in Doritos, the tortilla snack, can turn the skin invisible, scientists have found.
A chemical called tartrazine, also known as FD&C Yellow #5 and as the E number E102, was mixed with water and rubbed on the shaved stomach and scalp of lab mice. Moments later, the skin was transparent.
Tartrazine is found in a host of food products including cornflakes, sweets, energy drinks and chicken stock as well as crisps and is safe for consumption but has been linked to hyperactivity.
Experiments revealed that the skin’s appearance changed a few minutes after the orange solution was rubbed in. Blood vessels and organs could be seen a centimetre below the surface.
The groundbreaking discovery is the first time scientists have managed to remove the opacity of skin by modifying its refractive index – the amount light bends as it passes through something.
Illustration of skin tissues rendered transparent by tartrazine. Photo / US National Science Foundation
Study co-author Dr Zihao Ou, who conducted the research while at Stanford University and is now an assistant professor of physics at the University of Texas at Dallas, explained: “For those who understand the fundamental physics behind this, it makes sense. But if you aren’t familiar with it, it looks like a magic trick.
“It’s important that the dye is biocompatible – it’s safe for living organisms. In addition, it’s very inexpensive and efficient. We don’t need very much of it to work.”
It is hoped that by being able to easily peer below the skin, scientists will be able to use the technique to learn more about how the brain and other organs work, and to shed light on complex biological processes in the hope of treating a host of diseases.
And, unlike the unfortunate Jack Griffin in the classic HG Wells story The Invisible Man, the process is reversible and skin returns to normal when washed.
Current scientific work to see into living tissue is focused on minimising how much light is absorbed and scattered, and this has resulted in the ability to see about 2mm below the skin.
But the new approach has “blown the record out of the water by a factor of five”, according to Dr Christopher Rowlands, an Imperial College bioengineer and optical physicist who was not involved in the study.
The Doritos E-number changed skin transparency because it absorbs lots of blue light and when this is mixed with a liquid layer found naturally in the skin, known as the extracellular matrix, it increases the refractive index to an almost-perfect match for the skin cells and other components of the skin.
This then allows light to pass through all parts of the skin without being bounced around, the scientists found, leading to transparency.
Dr Ou explained: “We combined the yellow dye, which is a molecule that absorbs most light, especially blue and ultraviolet light, with skin, which is a scattering medium.
“Individually, these two things block most light from getting through them. But when we put them together, we were able to achieve transparency of the mouse skin.
“It takes a few minutes for the transparency to appear. It’s similar to the way a facial cream or mask works: The time needed depends on how fast the molecules diffuse into the skin.”
A jar of tartrazine dye. Photo / US National Science Foundation
The scientists say the process is not only more effective than current high-tech methods but also cheap, safe and easily accessible.
Dr Rowlands told the Telegraph that if the breakthrough was paired with other techniques, it could lead to a revolution in medical and scientific imaging.
He said: “It is one of those ideas that is really obvious when someone tells you. When I read the study I was kicking myself.
“Like all really good ideas, it is only obvious when somebody else tells you. I will be shocked if there are not at least a handful of studies out in the next year where somebody uses tartrazine and did exactly what they did before but got 10 times deeper penetration.”
The study is published in Science and has yet to be tested on human skin, which is 10 times as thick as that of a mouse, but it is thought it will likely be similarly effective.
